I want to get an array of grid column header names. I have tried to use grid.getGridColumns (http://docs.sencha.com/ext-js/4-0/#%21/api/Ext.grid.header.Container-method-getGridColumns) and this.getGridColumns (http://docs.sencha.com/ext-js/4-0/#%21/api/Ext.grid.header.Container-method-getGridColumns)() under the grid. But it gives me an error that it is not a function. How it is used?